Not Applicable
Not Applicable
The present invention relates to disc memory systems, and more particularly, to positioning information on magnetic disc media for positioning read/write heads.
During normal operation, most computer systems typically require high-capacity, non-volatile data storage resources. One such data storage resource is a disk drive. A disc drive operates by writing user data to, and reading user data from, a disc-shaped magnetic medium that is organized into tracks. Each track forms an annulus bounded by an inner radius and an outer radius on the disk, where the center of the annulus is the axis of rotation of the disk. In addition to the user data within the tracks, positioning information, known in the art as xe2x80x9cservo data,xe2x80x9d is typically written periodically among the user data within the tracks. Both the user data on the tracks and servo data between the tracks are magnetic markings written on the media by creating spatially varying magnetization patterns on the media. Read/write heads read data from and write data to the disc medium as the disc rotates about its axis of rotation. The servo data are used to guide the read/write heads to an appropriate position relative to the track being read from or written to.
FIG. 1 (Prior Art) shows a prior art head-disc assembly subsystem 10 of a magnetic disc memory system with an associated servo control system 20. A disc medium 30 attaches to a spindle motor 40, enabling rotation of the disc medium 30 about an axis of rotation. Multiple tracks 50 (centerlines only are shown) containing information data are written during a manufacturing process. A head 60 attached to a head arm assembly 70 is connected to a positioner assembly 80. The servo data from the disc medium 30 are read by head 60 and provided to the servo control system 20 after appropriate pre-amplification by pre-amplifier 76. The servo control system 20 analyzes the servo data and determines an appropriate correction, if necessary, to return the head to its optimum position over the track 50. The servo control system 20 communicates the head position correction to the positioner assembly 80 via an positioning signal 90. The positioner assembly 80 adjusts the position of the head 60 as a function of the positioning signal 90 from the servo control system 20.
FIG. 2 (Prior Art) shows a single track 50 from the disc medium 30 of FIG. 1, subdivided into intervals of user information 54 and position information 56. FIG. 3 (Prior Art) illustrates how position information 56 of FIG. 2 is further subdivided into a servo burst 58 and multiple fields 59 that contain Fill, AGC, INDEX, and ADDRESS information. These later multiple fields 59 are beyond the scope of the present invention, and are therefore not described further.
FIG. 4 (Prior Art) shows a more detailed view of the servo bursts 58 of FIG. 3, positioned along several adjacent segments 100 of the tracks 50 on a typical magnetic disc medium 30. Because the segments 100 are very short arcs of the circular tracks 50, they are shown in FIG. 4 as straight, without curvature. FIG. 4 shows that each individual servo burst 58 is offset both perpendicularly from the center of tracks 110 as well as along the track with respect to the adjacent servo bursts. The purpose of this arrangement is described below.
FIG. 5 (Prior Art) illustrates a read/write head 60 from the subsystem of FIG. 1, properly positioned directly over a track segment 100, about to encounter two servo bursts 58C and 58D. The disc medium 30 is spinning about an axis of rotation such that the track segment 100 is moving in the direction of the arrow 102, with respect to the head 60. The read/write head 60 is properly positioned over the track segment 100 when the head is situated symmetrically about the track center line 110 of the track segment 100, as shown.
As the servo bursts 58 pass under the read/write head 60, the head 60 converts the spatially varying magnetic patterns on the medium 30 that form the bursts 58, into time varying electrical signals (also referred to herein as the xe2x80x9cservo burst readback signalxe2x80x9d). FIG. 6 (Prior Art) illustrates electrical signal 120 and 130, corresponding to servo bursts 58C and 58D, respectively, that the read/write head 60 produces as it passes the bursts 58C and 58D. Since the head 60 overlaps equal portions of bursts 58C and 58D, the amplitudes of the resulting signals 120 and 130 are substantially equal. The servo control system 20 interprets the equal amplitudes of electrical signals 120 and 130 to mean the head 60 is optimally positioned, and therefore no improvement is necessary.
FIG. 7 (Prior Art) illustrates an example of an improperly positioned head 60 from the subsystem 10 of FIG. 1, which is perpendicularly offset from the track centerline 110 of the track 100. Since the head 60 overlaps more of burst 58C than burst 58D, the amplitude of the electrical signal 220 is greater than the amplitude of the electrical signal 230, as shown in FIG. 8 (Prior Art). The servo control system 20 interprets the discrepancy between the electrical signals 220 and 230 to mean that the head 60 is not optimally positioned about the centerline. The servo control system 20 generates a positioning signal 90 as a function of amplitude differential between the two electrical signals 220 and 230, and which of the two signals is larger. The amplitude differential indicates how much correction the servo control system 20 should apply to the head 60, and which of the two is larger indicates which direction the servo control system 20 should move the head 60.
FIG. 4 shows that four rows of servo bursts should be used (58A, 58B, 58C and 58D) to detect a positioning error and generate a positioning signal 90 to compensate this error. Bursts 58C and 58D are used to keep the head on track (within an error of +/xe2x88x92 one half of a track width), and bursts 58A and 58B are used to determine the direction to move the head 60 if the positioning error is greater than or equal to one half of a track width. Bursts must have substantial length (in the direction of track motion) to achieve an acceptable signal to noise ratio. Therefore a significant portion of the track must be dedicated to positioning information. The more that sectors of the disk 30 are used for servo information, the more important it is to reduce the size of bursts area in order to achieve best areal density in the magnetic recording.
FIG. 4 also shows that a substantial part of the disc area used for servo bursts area, nearly 50 percent, is not used at all. Large gaps between bursts in the direction perpendicular to the track centerline are necessary to avoid superposition of servo burst signals (i.e., crosstalk) from adjacent servo bursts. FIG. 4 thus shows that the prior art servo burst method suffers from significant area penalty. It is therefore desirable to realize a more efficient servo-burst method that will reduce the percentage of the track dedicated to servo bursts.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
The present invention provides a reduction in the percentage of the area dedicated to read/write head positioning information on a magnetic recording medium by employing servo bursts of different frequencies, thus allowing the servo bursts to be located adjacently in the direction perpendicular to the track center line (i.e., transverse to the center line). The servo burst readback signal corresponding to a particular servo burst on the disk medium is distinguished from the readback signal of an adjacent servo burst by analyzing the associated signal frequencies. Therefore, the invention requires little or no gap between servo bursts to prevent superposition of the readback signals from different bursts, as long as the adjacent bursts are of different frequencies. This allows writing bursts close to each other in the direction perpendicular to the track, so that crosstalk or even partial erasure of one burst by another is acceptable.
Specific layout of bursts and the associated frequency assignments may differ for different applications. In general, the prior art systems separate servo bursts in space on the disc media, which results in a separation in time when read by a head. This physical, spatial separation prevents superposition of the readback signal from different bursts. The present invention separates the servo bursts in frequency, so that spatial separation is unnecessary. The separation in frequency prevents superposition of the readback signal from different bursts.
The foregoing and other objects are achieved by the invention which in one aspect comprises a method of arranging a servo burst pattern for use in positioning a read/write head with respect to a track on a magnetic disc medium. The method includes disposing a first servo burst on the track, characterized by a first frequency, such that the first servo burst begins near a centerline associated with the track and extends in a first direction perpendicular to the centerline towards a first track edge. The method further includes disposing a second servo burst on the track, characterized by a second frequency, such that the second servo burst begins near the centerline and extends in a second direction perpendicular to the centerline towards a second track edge.
In another embodiment of the invention, the first servo burst extends beyond the first track edge to a centerline of a next adjacent track in the first direction. The second servo burst extends beyond the second track edge to a centerline of a next adjacent track in the second direction.
In another embodiment of the invention, the first servo burst is adjacent to the second servo burst, such that the first servo burst meets the second servo burst at the centerline.
Another embodiment of the invention further includes disposing a third servo burst on the track, characterized by the first frequency, such that the third servo burst is substantially centered on the centerline. The third servo burst is also offset from the first servo burst and the second servo burst in a direction parallel to the centerline.
In another embodiment of the invention, the third servo burst extends to the first track edge and to the second track edge.
In another embodiment of the invention, the third servo burst is adjacent to the first servo burst and to the second servo burst.
Another embodiment of the invention further includes disposing a fourth servo burst, characterized by the second frequency, on a next adjacent track in the first direction, and disposing a fifth servo burst, characterized by the second frequency, on a next adjacent track in the second direction.
In another embodiment of the invention, the fourth servo burst is centered on the next adjacent track in the first direction, and the fifth servo burst is centered on the next adjacent track in the second direction.
In another embodiment of the invention, the first servo burst includes a spatially varying magnetization pattern characterized by a first spatial frequency substantially equal to the first frequency. The second servo burst includes a spatially varying magnetization pattern characterized by a second spatial frequency substantially equal to the second frequency.
In another aspect, the invention comprises a servo burst pattern for use in positioning a read/write head with respect to a track on a magnetic disc medium. The burst pattern includes a first servo burst disposed on the track, characterized by a first frequency, such that the first servo burst begins near a centerline associated with the track and extends in a first direction perpendicular to the centerline towards a first track edge. The burst pattern also includes a second servo burst disposed on the track, characterized by a second frequency, such that the second servo burst begins near the centerline and extends in a second direction perpendicular to the centerline towards a second track edge.
In another embodiment of the invention, the first servo burst extends beyond the first track edge to a centerline of a next adjacent track in the first direction. The second servo burst extends beyond the second track edge to a centerline of a next adjacent track in the second direction.
In another embodiment of the invention, the first servo burst is adjacent to the second servo burst, such that the first servo burst meets the second servo burst at the centerline.
Another embodiment of the invention further includes a third servo burst, characterized by the first frequency, such that the third servo burst is substantially centered on the centerline. The third servo burst is also offset from the first servo burst and the second servo burst in a direction parallel to the centerline.
In another embodiment of the invention, the third servo burst extends to the first track edge and to the second track edge.
In another embodiment of the invention, the third servo burst is adjacent to the first servo burst and to the second servo burst.
Another embodiment of the invention further includes a fourth servo burst, characterized by the second frequency, on a next adjacent track in the first direction, and a fifth servo burst, characterized by the second frequency, on a next adjacent track in the second direction.
In another embodiment of the invention, the fourth servo burst is centered on the next adjacent track in the first direction, and the fifth servo burst is centered on the next adjacent track in the second direction.
In another embodiment of the invention, the first servo burst includes a spatially varying magnetization pattern characterized by a first spatial frequency substantially equal to the first frequency. The second servo burst includes a spatially varying magnetization pattern characterized by a second spatial frequency substantially equal to the second frequency.
In another aspect, the invention comprises a system for positioning a read/write head with respect to a track on a magnetic disc medium. The disc medium includes a servo burst pattern having a first servo burst disposed on the track, characterized by a first frequency, such that the first servo burst begins near a centerline associated with the track and extends in a first direction perpendicular to the centerline towards a first track edge. The servo burst pattern also includes a second servo burst disposed on the track, characterized by a second frequency, such that the second servo burst begins near the centerline and extends in a second direction perpendicular to the centerline towards a second track edge. The system includes a multi-frequency filter for receiving a composite readback signal from the read/write head and for separating the composite readback signal into a first readback signal and a second readback signal. The first readback signal corresponds to the first servo burst, and the second readback signal corresponds to the second servo burst. The system also includes an envelope detector for providing a first amplitude signal corresponding to an amplitude of the first readback signal, and for providing a second amplitude signal corresponding to an amplitude of the second readback signal. The system further includes a comparator for comparing the first amplitude signal to the second amplitude signal, and for providing an error signal corresponding to a difference between the first amplitude signal and the second amplitude signal. The system also includes a servo control system for receiving the error signal and generating a drive signal therefrom, and a positioner assembly, coupled to the read/write head, for adjusting the position of the read/write head with respect to the track, as a function of the drive signal.
Another embodiment of the invention further includes a band pass filter for receiving the readback signal from the read/write head, filtering an out-of-band noise component from the readback signal so as to produce a filtered readback signal, and providing the filtered readback signal to the multi-frequency filter.
In another embodiment of the invention, the multi-frequency filter includes a digital filter. The system further includes an analog to digital converter for receiving the readback signal from the read/write head, sampling the readback signal so as to produce a sequence of readback signal samples, and providing the readback signal samples to the digital filter.
Another embodiment of the invention further includes a servo gate generator for generating a servo gate. The servo gate is in an active state when the readback signal corresponding to one of the servo bursts is present, and in an inactive state when the readback signal corresponding to the servo bursts is absent.
In another embodiment of the invention, the multi-frequency filter receives the servo gate, and passes the first readback signal and the second readback signal when the servo gate is in the active state. The filter also blocks the first readback signal and the second readback signal when the servo gate is in the inactive state.
Another embodiment of the invention further includes a downconverter for receiving the readback signal, for shifting a frequency spectrum associated with the readback signal to a lower frequency range so as to provide a down-shifted readback signal, and for providing the down-shifted readback signal to the multi-frequency filter.
Another embodiment of the invention further includes an upconverter for receiving the readback signal, and for shifting the frequency spectrum associated with the readback signal to a higher frequency range so as to provide an up-shifted readback signal. The system also includes a downconverter for receiving the up-shifted readback signal, for shifting a frequency spectrum associated with the up-shifted readback signal to a lower frequency range so as to provide a down-shifted readback signal, and for providing the down-shifted readback signal to the multi-frequency filter.
In another aspect, the invention comprises a servo burst pattern for use in positioning a read/write head with respect to a plurality of concentric tracks on a magnetic disc medium, wherein each of the plurality of tracks is characterized by a centerline, an inside track edge and an outside track edge. The servo burst pattern includes a first set of servo bursts adjacently disposed on the tracks along a first axis perpendicular to the centerlines. Each of the first set of servo bursts is disposed on an individual track, from the inside track edge to the outside track edge. A frequency characteristic associated with each of the servo bursts alternates between a first frequency and a second frequency for consecutive servo bursts. The servo burst pattern also includes a second set of servo bursts adjacently disposed on the tracks along a second axis perpendicular to the centerlines and parallel to the first axis. Each of the second set of servo bursts is disposed on two adjacent tracks, from the centerline of one track to the centerline of a next adjacent track. A frequency characteristic associated with each of the second set of servo bursts alternates between the first frequency and the second frequency for consecutive servo bursts.
In another aspect, the invention comprises a system for positioning a read/write head with respect to a track on a magnetic disc medium. The disc medium includes a servo burst pattern having a first set of servo bursts adjacently disposed on the tracks along a first axis perpendicular to the centerlines. Each of the first set of servo bursts is disposed on an individual track, from the inside track edge to the outside track edge, and a frequency characteristic associated with each of the servo bursts alternates between a first frequency and a second frequency for consecutive servo bursts. The servo burst pattern also includes a second set of servo bursts adjacently disposed on the tracks along a second axis perpendicular to the centerlines and parallel to the first axis. Each of the second set of servo bursts is disposed on two adjacent tracks, from the centerline of one track to the centerline of a next adjacent track, and a frequency characteristic associated with each of the second set of servo bursts alternates between the first frequency and the second frequency for consecutive servo bursts. The system includes a multi-frequency filter for receiving a composite readback signal from the read/write head and for separating the composite readback signal into a first readback signal and a second readback signal. The first readback signal corresponds to servo bursts characterized by the first frequency and the second readback signal corresponds to servo bursts characterized by the second frequency. The system further includes an envelope detector for providing a first amplitude signal corresponding to an amplitude of the first readback signal, and for providing a second amplitude signal corresponding to an amplitude of the second readback signal. The system also includes a comparator for comparing the first amplitude signal to the second amplitude signal, and for providing an error signal corresponding to a difference between the first amplitude signal and the second amplitude signal. The system also includes a servo control system for receiving the error signal and generating a drive signal therefrom. The system also includes a positioner assembly, coupled to the read/write head, for adjusting the position of the read/write head with respect to the track, as a function of the drive signal.
In another aspect, the invention includes a method of positioning a read/write head with respect to a track on a magnetic disc medium. The disc medium includes a servo burst pattern having a first set of servo bursts adjacently disposed on the tracks along a first axis perpendicular to the centerlines. Each of the first set of servo bursts is disposed on an individual track, from the inside track edge to the outside track edge, and a frequency characteristic associated with each of the servo bursts alternates between a first frequency and a second frequency for consecutive servo bursts. The servo burst pattern also includes a second set of servo bursts adjacently disposed on the tracks along a second axis perpendicular to the centerlines and parallel to the first axis. Each of the second set of servo bursts is disposed on two adjacent tracks, from the centerline of one track to the centerline of a next adjacent track, and a frequency characteristic associated with each of the second set of servo bursts alternates between the first frequency and the second frequency for consecutive servo bursts. The method includes receiving a composite readback signal from the read/write head and separating the composite readback signal into a first readback signal and a second readback signal. The first readback signal corresponds to servo bursts characterized by the first frequency and a second readback signal corresponding to servo bursts characterized by the second frequency. The method also includes providing a first amplitude signal corresponding to an amplitude of the first readback signal, and providing a second amplitude signal corresponding to an amplitude of the second readback signal. The method further includes comparing the first amplitude signal to the second amplitude signal, and providing an error signal corresponding to a difference between the first amplitude signal and the second amplitude signal. The method also includes receiving the error signal and generating a drive signal therefrom, and adjusting the position of the read/write head with respect to the track, as a function of the drive signal.
In another aspect, the invention comprises method of positioning a read/write head with respect to a track on a magnetic disc medium, The disc medium includes a servo burst pattern having a first servo burst disposed on the track, characterized by a first frequency, such that the first servo burst begins near a centerline associated with the track and extends in a first direction perpendicular to the centerline towards a first track edge. The servo burst pattern also includes a second servo burst disposed on the track, characterized by a second frequency, such that the second servo burst begins near the centerline and extends in a second direction perpendicular to the centerline towards a second track edge. The method includes receiving a composite readback signal from the read/write head and separating the composite readback signal into a first readback signal and a second readback signal. The first readback signal corresponds to the first servo burst and the second readback signal corresponds to the second servo burst. The method also includes providing a first amplitude signal corresponding to an amplitude of the first readback signal, and providing a second amplitude signal corresponding to an amplitude of the second readback signal. The method further includes comparing the first amplitude signal to the second amplitude signal, and providing an error signal corresponding to a difference between the first amplitude signal and the second amplitude signal. The method also includes receiving the error signal and generating a drive signal therefrom, and adjusting the position of the read/write head with respect to the track, as a function of the drive signal.